JSON Formatter & Validator
Paste messy or minified JSON to get it validated and pretty-printed instantly. If the document is invalid you get the exact parser message so you can find the problem fast.
Output
Enter a value to see the result.
About this tool
The formatter uses the browser's native JSON parser, so what it accepts is exactly what your application will accept. Trailing commas, single quotes and comments are rejected — just like in a real API client.
Minify mode strips every optional space and newline, which is useful before embedding JSON in a config value or measuring payload size. Sorting keys alphabetically makes it far easier to diff two API responses.
Frequently asked questions
- Why is my JSON invalid?
- The most common causes are trailing commas, single quotes instead of double quotes, unquoted keys and comments. JSON permits none of these — the error message shows where the parser stopped.
- Does formatting change my data?
- No. Only whitespace changes. Key order is preserved unless you explicitly enable alphabetical sorting.
- Is there a size limit?
- There is no artificial limit. Very large documents (tens of megabytes) may be slow because everything is processed in your browser tab.
- Can I use it for JSON Lines or NDJSON?
- Not directly — each line must be validated separately, since a JSON Lines file is not itself a single valid JSON document.
- Is my JSON uploaded to a server?
- No. Parsing and formatting happen entirely on your device, so it is safe to paste internal API responses.